Lesson 3/Learning Event 2
As the handle of the brake valve is moved toward the applied
position, force is applied to the top of the pressure regulating
spring. When this happens, the spring and piston assembly move
downward and the exhaust valve seat engages the exhaust valve. This
closes the passage to the exhaust port. The exhaust and inlet
valves, being part of the same assembly, cause both valves to move
together. After the exhaust valve is closed and the piston assembly
continues to move downward, the inlet valve is forced off its seat.
This lets air pressure from the reservoir pass through the inlet
valve and out the brake chamber port to the connection leading to the
service line and the brakes on the trailer.
As soon as the air pressure below the piston assembly overcomes the
mechanical force on top of it, the piston assembly lifts and the
intake valve closes. The closing of the inlet valve stops the
airflow from the reservoir. The exhaust valve remains closed
preventing any loss of air through the exhaust port.
If the brake valve handle is moved farther toward the fully applied
position, it adds more mechanical force on top of the piston assembly
and increases the delivered air pressure.
If the brake valve handle is moved toward the released position, the
mechanical force on top of the piston assembly is decreased. The air
pressure below the piston assembly lifts it slightly, opening the
exhaust valve and permitting air pressure to exhaust from the service
line. When the air pressure under the piston and the mechanical
force on top of the piston is again equal, the exhaust valve will
close. When the brake valve handle is moved to the released
position, the intake valve is closed, the exhaust valve is opened,
all air pressure is exhausted from the brake cylinders, and the
brakes are released.
Another device in airbrake systems is the quickrelease valve. The
purpose of this valve, as the name suggests, is to speed up the
release of the applied brakes.
When air pressure from the brake valve enters the brake valve port of
the valve, the diaphragm moves down and closes the exhaust port. Air
pressure then goes around the outer edges of the diaphragm and flows
out the side connections (brake chamber ports) to the brake chambers.
This applies the brakes.